Wall at the Edge of the World by Amanda Cockrell
Wherever the Roman conquers, there he dwells.
Sometime during the beginning of the second century A.D., the Ninth Legion Hispana marched into the mists of Roman-occupied Britain and disappeared forever.
Rome erased their name and number from the legionary rolls, and so far no British farmer has turned up a buried graveyard with his plow, to show where they lie.
Perhaps they turned their backs on everything that was of their own world and melted into the native tribes. Perhaps they were ambushed and cut down. All we know for certain is that they vanished as surely as if the ground had opened to swallow them, taking with them their Eagle, the life and honor of the Legion, and leaving behind only a few men who happened to be detached from the Hispana when it marched out that day.
This novel is history as it may have happened, on the edges of that country where history turns into myth.